In the field of microelectronic devices, sensors, optical elements and electronic displays, the development of devices that are conveniently and relatively inexpensively produced with a relatively low failure rate is important.
A well-known method of production of such devices is photolithography. According to this technique, a negative or positive resist (photoresist) is coated onto the exposed surface of a substrate. The resist is then irradiated in a predetermined pattern, and irradiated (positive resist) or non irradiated (negative resist) portions of the resist are washed from the surface to produce a predetermined pattern of resist on the surface. This is followed by one or more procedures. For example, the resist may serve as a mask in an etching process in which areas of the material not covered by resist are chemically removed, followed by removal of resist to expose a predetermined pattern of the conducting, insulating, or semiconducting material on the substrate.
According to another example, the patterned surface is exposed to a plating medium or to metal deposition (for example under vacuum), followed by removal of resist, resulting in a predetermined plated pattern on the surface of the material. In addition to photolithography, x-ray and electron-beam lithography have found analogous use.
While the above-described irradiative lithographic methods may be advantageous in many circumstances, all require relatively sophisticated and expensive apparatus to reproduce a particular pattern on a plurality of substrates. Additionally, they generally consume more reactants and produce more by-products in collateral fabrication steps than is optimal. Further, they are relatively time-consuming.
A need exists in the art for a convenient, inexpensive, and reproducible method of etching a surface according to a predetermined pattern. The method would ideally result in patterns having features in the micron and submicron domain, and would provide for convenient reproduction of existing patterns.
The study of self-assembled monolayers (SAMs) is an area of significant scientific research. Such monolayers are typically formed of molecules each having a functional group that selectively attaches to a peculiar surface, the remainder of each molecule interacting with neighboring molecules in the monolayer to form a relatively ordered array. Such SAMs have been formed on a variety of substrates including metals, silicon dioxide, gallium arsenide, and others. SAMs have been applied to surfaces in predetermined patterns in a variety of ways including simple flooding of a surface and more sophisticated methods such as irradiative patterning and microcontact printing.
An example of a SAM that has been extensively studied and has been the subject of several patents is composed of a molecular species having a long-chain alkyl group and a thiol (—SH) group at one terminus. These SAMs are formed on metallic surfaces like gold, silver, copper, etc. For example, U.S. Pat. No. 5,512,131 to Kumar et al., describes patterned transfer of alkyl thiols to metallic surfaces such as gold. Other molecular species capable of forming SAMs on oxide surfaces usually contain, at one terminus, trichloro or trialkoxy silane groups that form covalent bonds with hydroxylated surfaces of metal oxides. The drawback of using silane-containing compounds is that these materials are very reactive, forming crosslinked structures in solution or on the surface of a stamp used for microcontact printing. Trichlorosilanes must be handled under an inert atmosphere to prevent their decomposition.
A general description of patterning is found in U.S. Pat. No. 5,900,160 to Whitesides et al. relating to methods of etching articles via microcontact printing.
Accordingly, a general purpose of the present invention is to solve problems associated with expense, complicated apparatus, and other complications associated with patterning nickel and doped nickel films for optical and electronic devices.
One object is to provide a method of conveniently and reproducibly producing a variety of SAM patterns on nickel oxide surfaces such as the native oxide surfaces of nickel and doped nickel films, the pattern having resolution in the micron domain, and being amenable to etching.
Another object of the invention is to selectively remove by etching, areas of the nickel oxide and underlying metal that are not covered and protected by the SAM.
As used herein in the description of the present invention, the expression “nickel oxide” shall mean and include native nickel oxide as well as nickel oxide which has been grown or deposited on nickel or other metal films.
Another general purpose of the invention is to provide electronic and optical elements and devices that are conveniently and inexpensively manufactured, and that are adaptable to a variety of systems.